1) Field of the Invention
The present invention relates to a cleaning composition that effectively cleans a photoresist film, a buried material, and a metallic residue, from a surface of a substrate. The present invention also relates to a method of cleaning a semiconductor substrate using the cleaning composition and a method of forming wiring on a semiconductor substrate using the cleaning composition.
2) Description of the Related Art
Semiconductor substrates are generally formed by depositing a dielectric layer (insulation layer) on substrates made of, for example, silicon. A patterned conductive layer (i.e., a wiring layer) is formed in the dielectric layer of the semiconductor substrate to form a wiring.
The layers or the films that are used to form the patterns, for example, the photoresist film, are removed after the films have performed their roles. These layers or the films are removed so as not to become an obstacle in the subsequent process. The layers or the films are removed using a stripping solution. The stripping solution is also used to remove residues of metal or the like in the process of wiring formation. Conventionally, compositions of the stripping solutions have been optimized for use according to a target film to be stripped and a target residue to be cleaned.
However, it has been quite complicated to prepare a variety of stripping solutions for each purpose. Furthermore, storage facilities and supply routes for preservation and use of the solutions have been required in respective cases, and therefore the dedicated facilities and devices have needed to be provided. As a result, the fabrication process of the semiconductor becomes costlier. Therefore, a stripping solution having high strippability and cleaning power and that is all-purpose has been required.
The inventors of the present invention worked toward the development of such a stripping solution. Consequently, the inventors found that a stripping solution containing a quaternary ammonium compound as a main component may be a required one.
However, with regard to the properties required for the stripping solution from the viewpoint of the semiconductor substrate, the conventional method has following problems.
Generally, in the semiconductor fabrication process, a photoresist film is removed through O2 plasma ashing or with an amine-based stripping solution, while in the method of forming multilayer interconnection using the damascene process, the buried material (which is also referred to as a sacrificed film) is removed with a hydrofluoric acid dilution after the photoresist film is removed.
The dielectric layer shields the wiring layer provided under the photoresist film and the buried material, and electrically insulates the wiring layer from another wiring layer. This dielectric layer is required to have a permittivity as low as possible in order to prevent influence thereof from being exerted on the electrical characteristics of the wiring layer. Among dielectric layers having a low permittivity, a particular dielectric layer having a permittivity k of 3.2 or less is becoming a mainstream.
However, a material (low-k material) having such a low permittivity is low resistant against O2 plasma ashing and the hydrofluoric acid dilution, and therefore the surface of the material easily deteriorates or the permittivity rises. Consequently, the electrical characteristic of the wiring layer is badly affected.
The inventors evaluated the stripping solution containing the quaternary ammonium compound as a main component. The inventors found that a lot of time is required to completely remove the photoresist film and the buried material when the stripping solution was used. The inventors concluded that the low-k material and copper (Cu) deteriorates because the treatment is performed for a long time.
The inventors prepared raw materials that could become components of the stripping solution and also some types of the same material, and prepared samples of the stripping solution by combinations of the types to evaluate stripping characteristics of the samples. The inventors found that some of the samples were excellent in the stripping characteristics and there was no bad effect on the surface of the low-k material. The inventors then analyzed these samples and found that these samples contained traces of potassium hydroxide (KOH). Therefore, the inventors concluded that if traces of KOH are added to the solution, it is possible to clean the substrates quickly without damaging the low-k material and Cu, and even the strippability is high.
The inventors studied the existing literatures to find out the reason why the existence of KOH in the stripping solution gave better results, what could be the best amount of the KOH, and what is the best method to adding the KOH. The inventors studied, for example, Japanese Patent Application Laid Open (JP-A) No. 2001-152190, U.S. Pat. Nos. 3,980,587, and 5,139,607. Consequently, the inventors realized that a stripping solution with the KOH has already been proposed. For example, the inventors realized that a cleaning solution for semiconductors containing KOH has been proposed in JP-A No. 2001-244228 and that a cleaning agent for integrated circuits containing KOH has been proposed in Japanese Patent (JP) No. 2836263.
However, in the stripping solution disclosed in JP-A No. 2001-152190, the KOH is exemplified only as one of candidate components selected from a fluoride-based reducing agent and a hydroxide-based reducing agent. Moreover, the problem described in JP-A No. 2001-152190 was solved by the composition that did not contain the KOH. In other words, the idea that a combination of at least the quaternary ammonium hydroxide, solution, water, anticorrosive, and KOH allows stripping characteristics to be improved without degradation of the surface of the low-k material, has been neither disclosed nor suggested. In addition, information required for actual use such as compositions for an optimal combination containing KOH as an essential component and each amount of the compositions, is not even suggested. Furthermore, strippability of the buried material is not clear from the publication.
In the compositions disclosed in the U.S. Pat. Nos. 3,980,587 and 5,139,607, as explained later, the amount of KOH is more that the upper limit of the same in the present invention. With that amount of KOH, however, it is quite impossible to remove the photoresist film or the like without degradation of the low-k material. Thus, the U.S. Pat. Nos. 3,980,587 and 5,139,607 do not solve the problem to be solved in the present invention.
Furthermore, with the technology disclosed in the JP-A No. 2001-244228 and JP No. 2836263, it is impossible to effectively remove the photoresist film or the like because components of a composition are different from those in the present invention. Moreover, the JP-A No. 2001-244228 and JP No. 2836263 do not solve the problem to be solved in the present invention.